1) Field of the Invention
The present invention relates to an image reading apparatus with improved image reading quality.
2) Description of the Related Art
An image reading apparatus comprises an optical unit that includes a light source for illuminating a paper document, a mirror for directing the reflected light from a paper document illuminated by the light source, a lens for forming an image of the reflected light directed on it, and a pulse motor for driving a scanning unit for reading the image on the document formed by the lens.
Moreover, in the image reading apparatus there is provided a low power-consumption mode and a normal power-consumption mode. In the normal power-consumption mode, power is supplied to almost all the parts of the image reading apparatus. On the other hand, in the low power-consumption mode, power is supplied to only the minimum necessary parts, such as a timer, a counter, and a memory, for a certain period of time.
In the image reading apparatus, there is a home position, which is a position of the optical unit when the optical unit is in a standby state for starting reading of a document, and a low power-consumption position, which is a position of the optical unit when the image reading apparatus is in the low power-consumption mode.
In the conventional image reading apparatus, the start position is the same as the low power-consumption position. As a result, when the image reading apparatus is in the low power-consumption mode, that is when the optical unit is in the low power-consumption position (which is same as the home position), paper dust that accumulates on a glass on which a paper document is kept for reading, tends to fall on the parts of the optical unit to thereby degrade the quality of the image reading. The paper dust accumulates on the glass while the paper is being transferred when performing reading operation. If a paper of poor quality is used then the amount of dust generated increases. Moreover, if the image reading apparatus is installed in an unfavorable environment like dusty place etc., this paper dust or other dust goes inside through small apertures around the glass and gets stuck on the mirror or other components of the optical unit thereby making it apt to generate faulty image having lines.